A cap made of synthetic resin material is often fitted to an opening of a container for liquids such as foods, drugs and cosmetics. The cap often consists of a primary cap having an outlet opening at a top wall thereof, and a secondary cap hinged thereto and adapted to close this outlet opening. For instance, Japanese utility model publication (kokai) No. 1-66355 discloses a container cap including a primary cap and a secondary cap which are joined together by a pair of flexible hinge strips having a reduced thickness, and also by a resilient piece so that the direction of the biasing force of the resilient piece may be reversed from the closing direction to the opening direction and vice versa depending on the angular position of the secondary cap. This utility model publication also discloses a plate member which is slidably guided on the top surface of the primary cap and provided with a tapered surface so as to allow the secondary cap to be opened up with a single hand by inwardly pushing the plate member which in turn pushes up the secondary cap with its tapered surface, the free end of the slide member simultaneously pushing the inner surface of the resilient piece to assist the effort to open the secondary cap.
However, this conventional arrangement involves a highly complex mechanism for opening the secondary cap, and is highly vulnerable to spillage or dripping of the content of the container because the content, which is often highly viscous, could interfere with the satisfactory operation of the sliding member when it gets into the sliding surfaces thereof. In particular, the slide member is provided with a slot through which an annular boss surrounding the outlet opening projects, and this part surrounding the annular boss tends to be soiled from spillage or dripping of the content.
Reference should be made to a copending U.S. patent application which was filed Sep. 6, 1995 (Our ref: F410), the contents of which are hereby incorporated by reference.